1. Field of the Invention
This invention relates to an improvement in a diaphragm type pump, and more particularly to a method of supplying a hydraulic operating fluid in a diaphragm type pump for preventing degradation of the pulsation rate and the volumetric efficiency.
2. Description of the Prior Art
In a diaphragm type pump, it is ideally desired that the fluid be pumped with 100% volumetric efficiency. In practical use, however, the volumetric efficiency cannot be raised over 99% and there is a pulsation rate of about 1%.
In the conventional diaphragm type pump, it is difficult to maintain the pulsation rate and the volumetric efficiency at such levels for a long period. As the operating time lapses, these performance factors are both degraded, that is the pulsation rate is raised and the volumetric efficiency is lowered.
For instance, when a latex fluid is pumped with the diaphragm type pump for 30 hours, the pulsation rate which is initially about .+-.1% is raised up to about .+-.5%, and the volumetric efficiency which is initially about 99% is lowered to about 94%. With the degradation of these factors, the discharge fluctuation is also increased from about 2% to about 5%.
The above-mentioned degradation is caused by the cavitation generated in the operating chamber as the plunger reciprocates to drive the diaphragm. The cavitation is generated every time the pressure within the hydraulic oil operating chamber is reduced as the plunger reciprocates and is accumulated therein as the operation is repeated for a long period.
The diaphragm type pump is suitable for pumping a material like latex which tends to aggregate by a shearing stress and is liable to choke spaces between slidable members in the pump, since the diaphragm type pump does not have any slidable portion which is in direct contact with the pumped fluid. Further, particularly when a highly accurate constant feeding of fluid is desired, the diaphragm type pump of hydraulic pressure type not of direct-acting type is preferred. However, the diaphragm type pump of hydraulic pressure type has a defect as mentioned hereinbefore in that the cavitation is accumulated within the operating chamber during a long period operation and the pulsation rate and the volumetric efficiency are degraded.
In order to solve the above problems inherent in the conventional diaphragm type pump of hydraulic pressure type, it has been known in the art to automatically supply an operating fluid to the operating chamber as well as deair the bubbles within the operating chamber as disclosed for instance in Japanese Utility Model Publication Nos. 43(1968)-15407, 45(1980)-29153 and 50(1975)-32121. These devices use only one valve for these purposes.
The above-mentioned conventional devices for conducting the deairing and oil supply by use of a single valve has a defect in that the accurate control of the amount of deairing and oil supply is difficult inpractice. In practical use, therefore, the above-mentioned conventional devices are insufficient in operation.